Changes in sensitivity of cholinoceptors and adrenoceptors during transhemispheric cortical reorganisation in rat SmI

The reorganisation of primary somatosensory cortex that occurs after lesion ing the corresponding cortex of the contralateral hemisphere in rat has bee n termed, 'transhemispheric cortical reorganisation'. Cholinergic and norad renergic innervations are hypothesized to be involved in cortical plasticit y. The present study investigated the change in responses of somatosensory neurones in the hindpaw representation area to muscarinic cholinoceptor and beta -adrenoceptor receptor stimulation, by iontophoretic application of a cetylchorine, noradrenaline, propranolol and atropine, during the process o f transhemispheric cortical reorganization at 3-4 days and at 20-21 days af ter lesioning the corresponding area in the contralateral hemisphere. Most neurones in control rats showed excitatory atropine-sensitive responses to acetylcholine, and inhibitory propranolol-sensitive responses to noradrenal ine. A marked reduction in neurones exhibiting muscarinic responses (from 6 9% to 22%) and beta -noradrenoceptor-mediated responses (from 62% to 24%) w ere seen in rats 3-4 days post lesion. The proportion of neurones respondin g had recovered by 3 weeks but the direction of the responses had changed w ith muscarinic response becoming predominantly inhibitory and beta -noradre noceptor responses predominantly excitatory. It is concluded that transhemi spheric cortical reorganization involves both receptor types and that the r eciprocal changes at different stages after injury maintain cortical plasti city. (C) 2001 Elsevier Science B.V; All rights reserved.